1. Field of the Invention
The present invention relates generally to radial flow impellers for use in centrifugal pumps and, more particularly, to an improved multiple-vane shrouded impeller that is constructed and arranged to allow the width between the impeller shrouds to be selected so as to obtain different optimum pump operating ranges for the same impeller components.
2. Background
As is well known in the art, impellers are utilized in centrifugal pumps to pressurize a flow of fluid. Standard impellers are typically of a fixed geometry which are designed and configured, along with the other pump components, for the pump to operate at peak efficiency at a specific pressure head and flow rate. The typical closed impeller has a pair of opposing shrouds or plates with a plurality of vanes or blades disposed between the opposing shrouds. The vanes are usually curved to facilitate radial discharge of the fluid, which enters the impeller at the center of the shroud. In the pump, the impeller is connected to a drive shaft mechanism that rotates the entire impeller assembly and is located in the pump casing. The volume of fluid that can flow through the impeller is fixed by the area defined by adjacent impeller vanes, the impeller wall and the opposing wall of the pump casing.
Currently, the typical process of making fabricated pump impellers is to utilize a front shroud that is substantially smooth across its inwardly facing surface and a back shroud that has a plurality of vanes protruding from its inwardly facing surface. The shrouds and vanes can be made by forming and welding, molding, injection molding, casting or die casting. During assembly of the impeller, the outer edge of the vanes are fixedly attached to the inwardly facing surface of the front shroud to form the flow channels between adjacent vanes. The vanes can be joined to the front shroud by fusion welding, brazing, sonic welding, friction or chemical adhesion. Once fixed, the impeller will put out a certain amount of flow for a given pump RPM and output head. Once the impeller is built, it is typically very difficult to change the operating characteristics because the width between the shrouds is fixed.
During the manufacturing process, the manufacturer typically makes a number of pump components that are suitable for selected pump sizes. For molded impellers, this requires a separate mold for each impeller width desired. As is well known in the art, molds are relatively expensive and have limited life. When the impeller components are put together, they are configured for a certain range of pump operating conditions. Because demand for certain size pumps can vary somewhat, the manufacturer must keep a significant inventory of impeller components on hand in order to meet anticipated and unanticipated needs for various size pumps. If the manufacturer anticipates incorrectly, it may find itself short of certain impeller components that are necessary to manufacture a specific size pump or be significantly overstocked on other impeller components that are configured for an unneeded size of pump. Either condition can create problems with meeting customer demands, increased costs to quickly manufacture needed parts and increased expenses from having an excessive inventory.
A number of patents provide pumps that are able to vary the flow characteristics by varying the width between the shrouds during the operation of the pump. Generally, they accomplish this by making at least one of the shrouds axially moveable relative to the other shroud. Such a pump is described in U.S. Pat. No. 4,417,849, which sets forth a pump having an impeller with two intermeshing impeller sections that are mounted on a common pump shaft such that one of the impeller sections is axially moveable relative to the other. The axial movement of the one impeller section, which is done in response to pump requirements, varies the width of the flow passage to decrease or increase the flow rate. A similar pump is described in U.S. Pat. No. 4,828,454, which discloses an impeller having an axially moveable shroud having a plurality of grooves for receiving the impeller vanes. The shroud moves to vary the flow passage width in response to system requirements. Another such pump is set forth in U.S. Pat. No. 5,211,530, which describes a two-piece impeller unit that includes an axially moveable shroud that has a plurality of radially extending grooves for receiving the impeller vanes in a meshing relationship and a plurality of axially extending grooves at its peripheral surface.
U.S. Pat. No. 2,358,744 discloses a centrifugal pump that varies the effective areas of the impeller blades on the two impeller sections. The pump capacity is varied by increasing or decreasing the overlap of the blades to increase or decrease the effective area of the impeller flow channel. U.S. Pat. No. 3,285,187 discloses an impeller for use in centrifugal pumps that utilizes rear and forward disks that both have blades thereon. When the two disks are joined together, the blades fill the space between the disks and form the flow channels therein. U.S. Pat. No. 3,918,831 discloses a variable impeller centrifugal pump having telescoping impeller sections. The driver impeller and the driven impeller operate together to form flow channels. The driver impeller is fixed to the pump drive shaft. An inducer varies the distance between the two driver and driven impellers to vary the pump characteristics. U.S. Pat. No. 4,412,783 discloses a centrifugal fan wheel having changeable pitch blades to control airflow independent of the speed of the fan.
Although the above described impellers and pumps,provide for variable flow rates during pumping operations, none of the above provide an impeller that can be fixedly set at various impeller widths during the manufacture of the pump that solves the problems associated with trying to anticipate customer needs for certain sized pumps. In addition, all of the above disclose relatively expensive pumps that are too costly for many types of very common pump uses, such as small circulating or centrifugal pumps utilized in home, business or industrial water circulation systems. Therefore, what is needed is an impeller that allows the manufacturer of the pump to fixedly select a desired impeller width from a single set of impeller components to substantially reduce pump component manufacturing, storage and inventory costs.
The variable width pump impeller of the present invention solves the problems identified above. That is to say, the present invention provides a pump impeller that can be configured into impellers of different fixed widths from the same impeller components so as to produce pumps having various operating characteristics. As such, the pump impeller of the present invention reduces the number of manufacturing molds that are needed to manufacture different impeller configurations and allows the manufacturer to substantially reduce its inventory of pump impeller components without risking having the components unavailable to meet demand for various sized pumps requiring different impeller widths.
In the primary embodiment of the present invention, the variable width pump impeller 10 is adapted to be rotationally mounted inside the housing of a centrifugal pump and is primarily comprised of a first impeller shroud having a first side and an opposite facing second side and a second impeller shroud also having a first side and an opposite facing second side. The second side of the first impeller shroud has a plurality of radially extending impeller vanes projecting axially therefrom. Each of the impeller vanes have an outer edge thereon. The first side of the second impeller shroud has a plurality of flat surfaces and a first set of grooves recessed therein. The plurality of axially recessed grooves that make up the first set of grooves are in alignment with the impeller vanes such that the vanes can be received by the grooves and be engaged therein in a meshing relationship. Once made, the impeller 10 can be configured by selectively joining the impeller vanes to either the flat surfaces or to the first set of grooves to form either a first flow channel (with the flat surfaces) or a second flow channel (with the first set of grooves) disposed between the second side of the first impeller shroud, the first side of the second impeller shroud and the impeller vanes for the passage of fluid to the pump outlet. The first flow channel will have a greater cross-sectional area than the second flow channel due to the greater effective impeller vane depth.
The typical pump impeller according to the present invention will also comprise an axial inlet in the second impeller shroud, a concavely frusto-conical surface leading into the axial inlet and a center hub in the first impeller shroud, the center hub being sized and configured to be at least partially disposed within the axial inlet when the first impeller shroud is joined to the second impeller shroud. For ease of joining the two impeller shrouds, one or more alignment pins on one or more of the impeller vanes and one or more corresponding alignment holes in one or more of the flat surfaces or the first recessed grooves can be utilized to ensure the two shroud pieces are properly aligned prior to fixedly joining them together.
In the preferred embodiment of the present invention, the first side of the second impeller shroud will have more than one set of grooves to allow the manufacturer to select the impeller depth that best matches the flow requirements of the pump utilizing impeller 10. For instance, the impeller 10 can have a second set of grooves, comprising a plurality of second recessed grooves, on the first side of second impeller shroud. Each of the second recessed grooves are axially recessed into the first side a second depth amount and angularly disposed along the first side of the second impeller shroud from one of the first recessed grooves. When the vanes are disposed in the second recessed grooves, the second side of the first impeller shroud, the first side of the second impeller shroud and the impeller vanes form a third flow channel for the passage of fluid therein. If the first depth amount is less than the second depth amount, the second flow channel will have a greater cross-sectional area than that of the third flow channel due to the greater effective vane depth.
Accordingly, the primary objective of the present invention is to provide a variable width pump impeller that is suitable for allowing the manufacturer to selectively choose between two or more fixed impeller widths from the same impeller components.
It is also an important objective of the present invention to provide a variable width pump impeller that has a plurality of vanes that can engage an equal number of flat surfaces or recessed grooves to provide flow channels of different vane depths.
It is also an important objective of the present invention to provide a variable width pump impeller that allows a manufacturer to reduce the number of molds necessary to manufacture impeller shrouds and to reduce the inventory of such impeller shrouds by providing an impeller that is suitable for selecting from a preset number of vane depths to obtain a fixed impeller width.
It is also an important objective of the present invention to provide a variable width pump impeller that has two or more fixed impeller vane depths and which can be made out of a variety of materials to obtain an impeller of fixed width.
The above and other objectives of the present invention will be explained in greater detail by reference to the figures and the description of the preferred embodiment which follows. As set forth herein, the present invention resides in the novel features of form, construction, mode of operation and combination of parts presently described and understood by the claims.